In this Aug. 6, 1945, file photo, survivors of the first atomic bomb ever used in warfare are seen as they await emergency medical treatment in Hiroshima, Japan. (AP Photo, File)

This post was originally written last year to mark the 70th anniversary of the U.S. nuclear attack on Hiroshima. It has been updated in conjunction with President Obama's visit to the shrine on Friday.

Seven decades ago, the United States dropped an atomic bomb on the Japanese city of Hiroshima. It almost instantly leveled most of the city and killed as many as 140,000 people. Three days later, on Aug. 9, another American bomber dropped a nuclear device on the city of Nagasaki, killing 40,000 to 80,000 people.

The devastation was followed by World War II's swift conclusion. It's seared into the collective global memory -- no other time in history has a nuclear weapon been used in war. The simple fact of the atomic bomb's awesome power went on to shape a half-century of Cold War geopolitics.

But what of the victims? Swaths of Hiroshima disappeared in a blistering flash, yet there were survivors. Here are some of the eyewitness testimonies of what took place on that terrible day in August 1945. (They have been gleaned from a number of oral historyprojects, all of which are easily accessible online.)

In this Sept. 8, 1945 file photo, only a handful of buildings remain standing amid the wasteland of Hiroshima, the Japanese city reduced to rubble following the first atomic bomb to be dropped in warfare. (AP Photo/File)

Yasuhiko Taketa was on his way to middle school, like many of the "hibakusha," or survivors of the atomic bombings in Hiroshima and Nagasaki who live to this day. At a train station, according to a speech he later delivered, he saw a "dazzling flash of light, brighter than even the sun," and then "an earsplitting roar" followed by a seismic explosion that shattered glass everywhere.

"My forehead felt hot, and I unconsciously touched it with my hand," narrates Taketa. "When I looked at the sky over Hiroshima, I saw a tiny, glittering, white object, about the size of a grain of rice, tinged with yellow, and red, which soon grew into a monstrous fireball. It was travelling in my direction, and I felt as though it was going to envelop me."

What I felt at that moment was that Hiroshima was entirely covered with only three colors. I remember red, black and brown, but, but, nothing else. Many people on the street were killed almost instantly. The fingertips of those dead bodies caught fire and the fire gradually spread over their entire bodies from their fingers. A light gray liquid dripped down their hands, scorching their fingers.

Those who found shelter after the explosion entered a strange, hideous world, where everyone's hair was literally fried and human shadows were etched onto stone.

A handout image made available by the US National Archives of smoke billowing 20,000 feet above Hiroshima while smoke from the burst of the first atomic bomb had spread over 10,000 feet on the target at the base of the rising column, in Hiroshima, Japan, 06 August 1945 (EPA/US NATIONAL ARCHIVES)

"I felt the city of Hiroshima had disappeared all of a sudden," said Akihiro Takahashi, a 14-year-old at the time in line for school, whose testimony was recorded by researchers in the late 1980s. "Then I looked at myself and found my clothes had turned into rags due to the heat. I was probably burned at the back of the head, on my back, on both arms and both legs. My skin was peeling and hanging like this."

Michiko Hachiya was then the director of a hospital in Hiroshima. He recorded the dazed, stumbling confusion of those still alive in the aftermath of the explosion. It was published in English in 1955.

"There were the shadowy forms of people, some of whom looked like walking ghosts. Others moved as though in pain, like scarecrows, their arms held out from their bodies with forearms and hands dangling," Hachiya wrote. "These people puzzled me until I suddenly realized that they had been burned and were holding their arms out to prevent the painful friction of raw surfaces rubbing together."

So many had, in an instant, lost those dearest to them. Eiko Taoka, then 21-years-old, was carrying her 1-year-old infant son in her arms aboard a streetcar. He didn't survive the day. "I think fragments of glass had pierced his head," she recounts. "His face was a mess because of the blood flowing from his head. But he looked at my face and smiled. His smile has remained glued in my memory."

An undated handout image released by the Hiroshima Peace Memorial Museum of the Hiroshima A-bomb Dome, originally the Hiroshima Prefectural Industrial Promotion Hall, photographed by US military following the atomic bomb drop on Hiroshima, Japan. (EPA/HIROSHIMA PEACE MEMORIAL MUSEUM)

Miyo Watanabe, then a volunteer at a steel factory, endured the initial blast by lying on her stomach. When she came to, she walked through a desolation.

...a woman lying dead at a house by the river bank, her neck stuck through with a piece of glass blown by the blast. The glass must have cut the artery. Blood was scattered around her. She had been suckling her baby. The baby was still absorbed in sucking the breast.

And she describes the horrific sights in makeshift hospital wards, where all the living victims ached with a desperate thirst:

They were delirious, begging for water. Those whose backs were burned lay on their stomachs, and those whose front was burned lay on their back. They could not even move to change their position. Their wounds and burns were covered with countless flies laying eggs there. Those eggs hatched into maggots, and these crawled all over their bodies causing them infernal agony.

Burn injuries were ubiquitous, recounts Hiroshi Sawachika, then a 28-year-old army doctor.

"The smell was quite strong," he said. "It's a sad reality that the smell human beings produce when they are burned is the same as that of the dried squid when it is grilled."

Sawachika tended to hundreds of patients that day, with limited knowledge of what to do. The exposure to radiation suffered by countless survivors would have a range of ill effects in the decades to come.

"I learned that the nuclear weapons which gnaw the minds and bodies of human beings should never be used," he concludes. "Even the slightest idea using nuclear arms should be completely exterminated."

Archive footage from the plane that dropped 'Little Boy' on the Japanese city of Hiroshima on August 6, 1945 and the aftermath of that detonation. (Internet Archive)